This invention relates to a hydrostatic steering system having an axially shiftable valve piston rotatably mounted in a steering gear housing to control distribution of pressurized fluid to a fluid powered steering motor.
A steering system of the foregoing type, described for example in German Pat. OS No. 27 12 290, has a rotor gear pump acting as a fluid metering device and a high pressure pump acting as a hydrostatic power source. The gear pump, also referred to as a hand-operated pump, is supplied with the pressurized fluid through annular grooves in response to angular displacement and axial shifting of the valve piston by a driver pin fixed to the steering spindle. Depending on the direction of rotation of the steering spindle, one of the pressure chambers associated with an operating cylinder motor is pressurized in order to effect power operated vehicle steering. Passage bridging cavities between cooperating annular grooves in the valve piston and passages in the steering gear housing, serve as control edges and to seal high and low pressure regions from each other. Leakage losses are unavoidable in the steering mechanism of the aforementioned type. The leakage losses result from a fluid coated peripheral surface on the valve piston and depend on the diameter and width of the passage bridging cavity.